Conventional manufacturing of continuous glass filament involves a continuous, integrated process in which combinations of mineral raw ingredients are blended and fed into large furnaces where they are melted, conditioned, and eventually delivered to multi-hole bushings from which fibers are drawn. Typical raw ingredients include limestone (CaCO3) and quartz sand (SiO2). In the glass furnace limestone first decomposes to form lime (CaO). The lime then reacts with quartz sand to form calcium silicates such as calcium metasilicate (CaSiO3). In addition, clays such as kaolin, are typically used as a source of aluminum as well as silicate. The clays typically used contain significant amounts of water which must be removed before the aluminum and silica can react.
To produce a high quality glass melt of sufficient homogeneity for high-efficiency fiber production, it is necessary that sufficient mixing of the various batch components, melting of those components, and mixing of the produced melt be allowed to occur. This can prove difficult using current technology, particularly at high throughputs and production rates.
One major problem with current technology is that glass furnaces do not do an efficient job of blending and mixing glass raw ingredients. Current technology thus requires long residence times and consumes significant amounts of energy, both of which substantially increase the cost of producing continuous glass fibers.
Further, carbon dioxide and other volatile materials form in the glass furnace from the decomposition of raw ingredients such as limestone and borates. This creates a troublesome foam within the glass furnace that increases the energy requires to form a homogeneous glass melt.
It would be desirable to provide a method for producing glass that does not require that the mixing of raw ingredients and the melting down of ingredients into a homogeneous melt occur simultaneously. It would also be desirable to provide a method in which decomposition of limestone occurs outside the glass furnace such that the volatile foam discussed above does not form within the glass furnace.